Microwave-assisted Pechmann reaction on P2O5/molecular sieves. Application to the preparation of 4-substituted coumarins

Article abstract of DOI:10.1080/10426500214886

4-Substituted coumarins were efficiently and rapidly synthesised via Pechmann condensation of phenols with ethyl acetoacetate catalyzed by P₂O₅/molecular sieves in satisfactory yields.

Full text of DOI:10.1080/10426500214886

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Phosphorus, Sulfur, and Silicon and the Related
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Microwave-Assisted Pechmann Reaction on P 2 O 5 /
Molecular Sieves. Application to the Preparation of 4-
Substituted Coumarins
Abbas Shockravi a , Hassan Valizadeh a & Majid. M. Heravi b
a Teacher Training University , Tehran, Iran
b Azzahra University , Vanak, Tehran, Iran
Published online: 27 Oct 2010.
To cite this article: Abbas Shockravi , Hassan Valizadeh & Majid. M. Heravi (2002) Microwave-Assisted Pechmann Reaction on
P 2 O 5 /Molecular Sieves. Application to the Preparation of 4-Substituted Coumarins, Phosphorus, Sulfur, and Silicon and the
Related Elements, 177:12, 2835-2841, DOI: 10.1080/10426500214886
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Phosphorus, Sulfur and Silicon, 2002, Vol. 177:2835–2841
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Copyright 2002 Taylor & Francis
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DOI: 10.1080/10426500290146875
MICROWAVE-ASSISTED PECHMANN REACTION ON
P2O5/MOLECULAR SIEVES. APPLICATION TO THE
PREPARATION OF 4-SUBSTITUTED COUMARINS
Abbas Shockravi,a Hassan Valizadeh,a and Majid. M. Heravib
Teacher Training University, Tehran, Irana
and Azzahra University, Vanak, Tehran, Iranb
(Received May 10, 2002)
4-Substituted coumarins were efficiently and rapidly synthesised via
Pechmann condensation of phenols with ethyl acetoacetate catalyzed
by P2O5/molecular sieves in satisfactory yields.
Keywords: Microwave irradiation; molecular sieves; Pechmann reac-
tion; P2O5
Coumarins stand in special place in the realm of synthetic organic
chemistry and natural products. Coumarins are common in nature
and used as intermediates in the synthesis of pharmaceuticals,1
insecticides,2 fluorescent brightness,3 and anticoagulant agents.4
Coumarins have been synthesized by many different routes,5 includ-
ing Pechmann reaction.6 In this reaction, substituted phenols are con-
densed with -ketonic esters in acidic media to afford coumarins. Var-
ious acidic media have been used to carry out this reaction.7 These
methods have their own merits and advantages. In some methods the
reactions need several hours or even days to be completed as should
be heated above 150 C. In addition some undesired products such as
chromones are reported to be formed during the reaction.8 Some meth-
ods also suffer from having tedious work-up procedure.
The microwave enhanced chemical reactions in solventless system
have gained popularity9 as they can be conducted efficiently and rapidly
to afford pure products in quantitative yields.
Although we did not have any accident using P2O5 in microwave oven, it is highly
recommended that the reaction should be carried out in an efficient hood.
Address correspondence to M. M. Heravi, Department of Chemistry, School of Sci-
ences, Azzahra University, Vanak, Tehran, Iran. E-mail: mmheravi@azzahra.ac.ir
2835

2836
A. Shockravi et al.
In this communication we report on the synthesis of coumarins
via Pechmann condensation of phenols and ethyl acetoacetate using
˚
P2O5/molecular sieves 3 A under microwave irradiation in a solvent-
less system.
Surprisingly, a survey of the literature revealed that the synthesis of
coumarins via Pechmann condensation of phenols with ethyl acetoac-
etate using solid support and microwave irradiation has received little
attention in the past. In best of our knowledge there are two methods
for the preparation of analogs of 2 that have been reported. Acceleration
of the Pechmann reaction by microwave irradiation using concentrated
H2SO4 has been reported by Kad et al.10 In another procedure devel-
oped by Li et al.,11 montmorillonite clay has been used as a catalyst in
a thermal reaction.
In view of the current emphasis on solid state synthesis12 and on
green chemistry13 there is a merit developing a solventless prepara-
tion of coumarins using an inexpensive and nonpolluting catalyst. We
˚
recently have used 3 A molecular sieve as promoting agent in regios-
elective synthesis of syn-oximes.14 In continuation of our interest in
conducting of organic synthesis in solventless system under microwave
irradiation15 we report an alternative method for the preparation of
˚
coumarins 2 using P2O5 supported on molecular sieve 3 A under mi-
crowave irradiation (Scheme 1).
SCHEME 1
The reaction is conducted by exposure of a mixture of phenolic
˚
compounds, P2O5 and molecular sieve 3 A to microwave irradiation.

Microwave-Assisted Pechmann Reaction on P O /Molecular Sieves
2837
2
5
Most of the phenolic compound disappeared within the first 4 min as
determined by TLC. It is nothworthy to mention that in the absence of
˚
molecular sieve 3 A the reactions are slugish and considerable amounts
of starting materials are recovered unchanged even ofter prolonged ex-
posure to microwave irradiation. Other types of solid supports were also
˚
used in this procedure but molecular sieve 3 A were found to give the
best yields.
It is also worthwhile to mention that in any cases no undesired prod-
ucts like chromans in addition to coumarins were detected.
In conclusion, we have developed an alternative procedure for the
fast and releatively eco-friendly preparation of coumarins. This method
features mild reaction condition, high yields and easy work-up proce-
durs. We beleive this strategy will find utility in organic synthesis.
EXPERIMENTAL SECTION
˚
Molecular sieves 3 A power was purchased from Merck chemical com-
pany. MP(s) were recorded on Stuart scientific apparatus and are uncor-
rected. 1H-NMR spectra were recorded on 60 MHz Bruker using TMS as
an internal standard and IR spectra were obtained from Perkin-Elmer
model 543 using KBr disc.
General Procedure
An appropriate phenol (14 mmol), ethyl acetoacetate (14.5 mmol), P2O5
˚
(14 mmol) and molecular sieve 3 A (2 g) were mixed throughly using a
spatula in a beaker. The beaker was placed in an house hold microwave
oven. The progress of reaction was monitored by TLC. The residue was
taken up in hot ethanol:acetone 50:50 and filtered. The filtrate was
evaporated to dryness and the crude was crystallized from suitable
solvent (Table I).
Selective Spectroscopic Data for 2a
1H-NMR (DMSO d6): 2.65 (s, 3H, Me), 6.4 (s, 1H, olefinic CH), 6.9–
7.7 (m, 3H, aromatic protons), OH is unobserved, IR, (KBr disc): up
1
to 3000 (OH broad), 1690 cm
.
Selective Spectroscopic Data for 2b
1H-NMR (DMSO d6): 2.6 (s, 3H, Me), 2.95 (s, 3H, Me), 6.35 (s, 1H,
olefinic CH), 6.8–7.6 (m, 2H, aromatic protons), OH is unobserved, IR,
1
(KBr disc): up to 3000 (OH broad), 1685 cm
.

2838

2839

2840
A. Shockravi et al.
Selective Spectroscopic Data for 2c
1H-NMR
(CDCl3): 2.59 (s, 3H, Me), 4.2 (s, 3H, OMe), 6.5 (s,
1H, olefinic CH), 7–7.5 (m, 3H, aromatic protons), IR, (KBr disc):
1
1685 cm
.
Selective Spectroscopic Data for 2d
1H-NMR (CDCl3): 2.62 (s, 3H, Me), 2.8 (s, 3H, Me), 6.4 (s, 1H, olefinic
1
CH), 7.1–7.6 (m, 3H, aromatic protons), IR, (KBr disc): 1685 cm
.
Selective Spectroscopic Data for 2e
1H-NMR (CDCl3): 1.7 (t, 3H, Me), 2.5 (s, 3H, Me), 4.3 (q, 2H, OCH2),
6.45 (s, 1H, olefinic CH), 7.2–7.8 (m, 3H, aromatic protons), IR, (KBr
1
disc): 1730, 1650 cm
.
Selective Spectroscopic Data for 2f
1H-NMR (CDCl3): 2.65 (s, 3H, Me), 5.5 (s, 2H, CH2), 6.5 (s, 1H,
olefinic CH), 7–8.2 (m, 8H, aromatic protons), IR, (KBr disc): 1700,
1
1630 cm
.
Selective Spectroscopic Data for 2g
1H-NMR (CDCl3): 1.9 (d, 3H, Me), 2.6 (s, 3H, Me), 2.9 (s, 3H, Me), 5.1
(q, 1H, aliphatic CH), 6.6 (s, 1H, olefinic CH), 7.1–7.8 (m, 3H, aromatic
1
protons), IR, (KBr disc): 1730, 1690 cm
.
Selective Spectroscopic Data for 2h
1H-NMR (CDCl3): 1.8 (d, 3H, Me), 2.6 (s, 3H, Me), 2.9 (s, 3H, Me),
3.1 (s, 3H, Me), 5.1 (q, 1H, aliphatic CH), 6.6 (s, 1H, olefinic CH), 7.1–7.8
(d, 1H, aromatic CH), 7.6 (d, 1H, aromatic CH), IR, (KBr disc): 1730,
1
1685 cm
.
Selective Spectroscopic Data for 2i
1H-NMR (CDCl3): 2.6 (s, 3H, Me), 2.8 (s, 3H, Me), 5.7 (s, 2H, CH2),
6.3 (s, 1H, olefinic CH), 7.1–8.4 (m, 7H, aromatic protons), IR, (KBr
1
disc): 1710, 1685 cm
.
Selective Spectroscopic Data for 2j
1H-NMR (CDCl3): 2.71 (s, 3H, Me), 6.5 (s, 1H, olefinic CH), 7.5–8.9
1
(m, 6H, aromatic protons), IR, (KBr disc): 1690 cm
.
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